Classic schwannoma showing Antoni A and Antoni B regions (photomicrograph)

Subclavian steal

With hemodynamically significant subclavian artery stenosis proximal to the takeoff of the vertebral artery, there is a compensatory shunting of blood from the ipsilateral vertebral artery to supply the arm, thus, “stealing” blood from the vertebrobasilar system. A minority of patients may have ischemic symptoms referable to the posterior circulation or the arm. In some cases, neurologic symptoms may be precipitated by ipsilateral arm exercise, head turning, or standing up.